MILWAUKEE -- Wisconsin voters are evenly split in their opinions of three Badger State politicians who face re-election next year: Gov. Scott Walker, House Speaker Paul Ryan and U.S. Sen. Tammy Baldwin.

Walker and Baldwin face no credible challengers, though several potential candidates have said they're considering making bids. Ryan, on the other hand, will face Democratic and Republican opposition next year.

Governor Scott Walker approval rating

Walker's approval rating stood at 48 percent in last week's Marquette University Law School Poll. It's the high-water mark in a slow, 18-month-long improvement in the governor's approval since it bottomed out when he quit the presidential race in fall 2015.

Governor Scott Walker

"He’s in better shape than he was," poll director Charles Franklin said. "Now, he’s not up to a net positive approval rating, so he has a ways to go."

Walker's approval had fallen to 37 percent in September 2015, when 59 percent of Wisconsin voters disapproved of the job he was doing in the state.

Franklin said Walker's current numbers are the governor's best showing in the MU Poll since October 2014, shortly before he won re-election to a second term.

Governor Scott Walker approval rating

But Scot Ross, who leads the liberal group One Wisconsin now questioned the poll's accuracy.

Scot Ross

"Opinions haven't changed of Scott Walker," Ross wrote after the poll's release. "Walker is 'more popular' only because the Marquette Poll interviewed more Republicans."

The poll, conducted at random of 800 registered Wisconsin voters, had a more Republican sample this time. Franklin said he wasn't sure if it was the start of a trend, or simply a "fluke."

Walker has he's ready to run again, and no credible Democrats have announced plans to challenge him.

State Sen. Kathleen Vinehout, D-Alma, set up a campaign committee last month, then said she still hasn't decided whether to actually run. State Rep. Dana Wachs, Milwaukee businessman Andy Gronik and Madison Mayor Paul Soglin are among several possible candidates.

Baldwin also has a dead-even favorability rating: 38 percent of voters view her positively, and 38 percent are negative on the first-term senator, according to the MU Poll.

Senator Tammy Baldwin approval rating

Plenty of Republicans are considering launching a challenge against Baldwin in 2018, but none are formally in the race.

This week, Nicole Schneider of Green Bay said she wouldn't run, according to the Associated Press. Schneider is the daughter-in-law of the man who once led Schneider National Trucking and could've spent significant sums of money on the campaign.

Ryan is presiding over a divided U.S. House of Representatives and narrowly passed an Affordable Care Act replacement bill this spring.

Paul Nehlen, a Trump-inspired Republican who lost by 68 points to Ryan in the 2016 primary, has announced he will challenge the speaker again next year. Democrats Cathy Myers, Randy Bryce and David Yankovich are also running.